There are red dot sights that are night vision compatible, they usually start at the $600 range and go on up from there. The night vision that you have to buy to use with then is considerably more expensive.

Thermal imaging devices do not work the same way. You can buy a thermal optic, but I have never seem one that could be mounted behind a red dot sight. I have also never seen a thermal gun sight that was any less than $2500.